Projectile guidance recording system

ABSTRACT

An instrument package (or telemeter) designed to be carried by a projectileuring test flights thereof and to process and record performance and/or meterorological data during such flights. The data is obtained from a plurality of on-board sensors and after signal conditioning the sensor outputs are sequentially sampled and the samples digitized before storage in memory. The stored data may be easily recovered after the projectile impacts by means of a portable interrogator unit. The package is designed to withstand the shock of the projectile&#39;s firing, flight, and impact.

The invention described herein may be manufactured, used and licensed byor for the Government for governmental purposes without the payment touse of any royalties thereon.

BACKGROUND OF THE INVENTION

This invention relates to telemetry systems and more particularly tosuch systems which can be used to gather in-flight data on theperformance of weapons such as guided missiles, artillery shells, "smartbombs" and other similar projectiles. Samples of such projectiles areoften withdrawn from service and subjected to flight tests to evaluatethe performance of such things as fuzes, arming circuits, guidancesystems, or to measure trajectory. Also, during development of weaponsof these types, test firings are made to evaluate performance bymeasuring such things as rate of rotation, vibration, stress, and otherfeatures. Also, environmental data such as meteorological data is oftengathered during such flight tests. The recent introduction ofsophisticated weapons such as "smart bombs" and projectiles has lead toan increase in the amount of on-board sensor data which must be gatheredduring such test flights.

Prior to the present invention there were two principal methods ofgathering such in-flight data. One was a hardwired telemetry system inwhich data was transmitted by wires from the projectile as it was beinglaunched or fired. The wires would be severed before the projectile leftthe gun barrel and no further data could be obtained thereafter. Thismethod has obvious disadvantages and limitations.

The more common prior art practice was to transmit the in-flight data toa ground station by radio. This is known as RF telemetry. However, RFtelemetry has numerous disadvantages, for example it requires atransmitter with numerous subcarrier oscillators for transmitting theoutputs of each sensor. Also, the bandwidth of the transmitter limitsthe amount of data which can be transmitted. Thus, high frequencyvibrational data which exceeds the transmitter's bandwidth cannot betelemetered by this means. Also, the projectile must be modified toinclude the transmitting antenna. RF telemetry also requires complex andexpensive manned ground station equipment for receiving and recordingthe transmitted data. Also, the transmission of the data means thatunauthorized parties can intercept it.

The present invention comprises a telemeter system which is designed tobe temporarily installed in the projectile under test and which includescircuitry for processing and recording, in a digital memory, all of thedata from the sensors carried by the projectile. The development of verylarge-scale integrated memory chips which have large storage capacityand which also can easily be made shock and vibration resistant has madefeasible the in-flight recording of data on projectiles of these types.After the flight, the projectile is recovered and the instrument packagetherein is interrogated and the data stored in the telemeter's memory istransferred to a light-weight portable recording instrument. The memorytelemeter can be packaged in a case which includes all of the requiredcircuitry and a battery and which is designed to withstand and functionduring the highshock conditions of firing, flight, and target or groundimpact. This memory telemeter is simpler, less expensive, lighter inweight and more accurate than the RF telemeters described above.

Such a memory telemetry system is especially useful in artilleryprojectile instrumentation. It is a self-contained, shock resistant,light-weight package, usually a cylinder, which may be located in anypart of the projectile. Required shell modifications are minimal and theaerodynamic characteristics of the round are virtually unaltered. As apractical matter, the warhead of an explosive shell or missile will beremoved for the test and the instrument package of the present inventioninserted in its place.

SUMMARY OF THE INVENTION

The invention comprises an instrument package, or a digital memorytelemeter, designed to be carried by a projectile as it is test fired,said telemeter comprising means to receive data from a plurality ofsensors carried by the projectile under test and means to sequentiallysample the outputs of said sensors and further means to digitize saidsampled outputs of said sensors and to store in a solid state digitalmemory such digitized data. This digitization may involve convertinganalog voltage levels from the sensors to binary coded numbers which canbe stored in memory.

The invention also comprises an instrument package comprising a casewhich preferably in the shape of a cylinder with a flexible circuitboard rolled up and inserted inside of said cylinder, with a battery andone or more sensors located inside of said rolled circuit board. Thepackage may be filled with a suitable potting compound which fills upall of the empty space inside of the cylinder, with an electricalconnector at one end of the cylinder, to facilitate connection toexternal sensors and the reading out of the data in memory after theprojectile has been recovered. Individual components mounted on thecircuit board are hardened for shock resistance.

The invention also comprises novel circuitry for processing and storingin-flight data from a plurality of on-board sensors. Such circuitry maycomprise, for example, signal conditioning circuitry, on-boardprocessing circuitry, a multiplexer for sequentially sampling theoutputs of said plurality of sensors, an analog-to-digital converter forconverting said sampled outputs to digital form suitable for storage ina digital memory of the type used in computers, as well as controlcircuitry such as an arming circuit and an electronic switch.

It is thus an object of the invention to provide improved apparatus forobtaining in-flight sensor data from sensors mounted on projectiles ofthe type described.

Another object is to provide a novel shock resistant, light-weight,compact, inexpensive instrument package which can be easily mounted in aprojectile to record in a digital memory the outputs of a plurality ofon-board sensors which are arranged to sense the performance of saidprojectile.

A still further object of the invention is to provide an improvedtelemetry system for projectiles which does not require a transmitter,subcarrier oscillators, an antenna, or complex and expensive mannedground station equipment.

These and other objects and advantages of the invention will becomeapparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of illustrative circuitry which may comprisethe present digital memory telemeter.

FIG. 2 is a block diagram showing more detail of the multiplexer of FIG.1.

FIG. 3 illustrates the output of the multiplexer of FIG. 2.

FIG. 4 shows the output of the analog-to-digital converter of FIG. 1.

FIG. 5 shows the rolled flexible circuit board on which the circuitry ofFIG. 1 may be mounted, before it is inserted into its cylindrical case.

FIG. 6 shows the complete instrument package mounted in its case.

FIG. 7 is a plan view of the circuit board before it is rolled up.

FIG. 8 shows the portable recording unit which is used to recover thedata after impact.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The cost of firing test rounds of sophisticated projectiles is rapidlyincreasing, as well as the amount of data required for later evaluationof projectile performance. Thus, there is a need for development of atelemetry system which can obtain as much data as possible from eachtest firing at a minimal cost per unit of data, utilizing a compact andlightweight instrument package. The present invention provides such asystem. In order to handle additional data with the apparatus of thepresent invention one may stack the memory chips or ICs to providealmost any desired memory capacity. Thus, large numbers of sensors canbe accommodated, or high frequency, wide bandwidth information from asmaller number of sensors can be rapidly scanned or sampled and theresultant large number of data samples stored in the memory for recoveryafter the projectile has impacted. Subsequent ground processing of therecovered data samples can result in a synthesis of the original analogwaveform which actuated the sensor.

The instrument package of the present invention may be included in sucha package or telemeter as shown in FIGS. 1 and 2. In FIG. 1, six leads,a-f, are shown coming from an equal number of sensors which are alllocated at various places on the projectile. Some of these sensors maybe within the instrument package case and others may be externallylocated. Each of the six leads, a-f, is applied to the signalconditioning circuits 5, which comprises separate channels, 5a-5f, foreach of the connected sensors. The signal conditioning circuitry isconventional and performs such functions as filtering, amplification,and attenuation of the analog signals received from the connectedsensors. The on-board processing circuits 7 are optional and can be usedto process the sensor output signals in its six separate channels,7a-7f. For example, circuits 7 may be designed to eliminate unwanted orredundant data which would occupy needed memory capacity. Thisprocessing circuitry for example might comprise threshold circuits foreliminating signals below or above threshold amplitudes. If desired, theprocessing circuitry 7 can be integrated with the signal conditioningcircuits 5. The six analog sensor signals or voltages, a-f, at theoutput of the processor circuits 7 are applied to multiplexer 9, whichis a device for sequentially sampling the voltage on each of its inputleads a-f and producing a single waveform which varies in stepwisefashion according to the instantaneous values of the sensor signals asthey are sampled. FIG. 2 shows in more detail how this can beaccomplished by means of a plurality of transmission gates, labelledgate #1 through gate #6, each of which receives a different one of thesensor output voltages from leads a-f. A six stage register 41 has sixoutputs 41a-41f, only one of which will have a binary one or a voltageat its output at any one time, and the register 41 is connected to andstepped by clock 23. Thus the gates will be sequentially enabled by thesignals on leads 41a-41f to sequentially sample the sensor outputs. Theoutputs of all the gates are tied together to form the output lead 11.The signal on lead 11 may appear as shown in FIG. 3 for two frames (ortwo cycles) of operation of the multiplexer. The voltage levels a-ftherein represent the sensor voltages when that sensor's gate isenabled, thus applying the sensor voltage from one of the multiplexerinput leads a-f to output lead 11. It can be seen that the voltagelevels of FIG. 3 for the second frame are somewhat different from thoseof the first frame, caused by the changing of the sensor output betweenthe sampling times of the two frames. The frame rate would be related tothe bandwidth or highest frequency component in the sensor output,according to well known principles.

The analog-to-digital converter 13 converts each one of the samplevoltage levels on lead 11 to a binary digital number representing thesampled voltage level. For example, an 8 bit analog-to-digital converterwould be capable of discriminating 256 different voltage levels andconverting them to digital form. Such an 8 bit binary digital number isrepresented in FIG. 4. This number is 10010110 or 150 in decimalnotation. Such a binary digital number is in proper form for storage ina digital memory such as memory blank 17, which is connected to theoutput of converter 13 via lead 15, and has output lead 19 forfacilitating the reading out of the data in the memory. The term memorybank is used to indicate that it may comprise a number of stacked memorychips or ICs to achieve the required memory capacity. For example, in aprototype telemeter constructed by the present inventors, the digitalmemory bank 17 comprised one or more low power, static random-accessmemory (RAM) ICs, each with a 64 kilobit capacity. Future availabilityof higher capacity memories will result in higher storage capacity ofthis instrument, or the same storage capacity for fewer components.

Static RAMs of the type preferred in the memory bank of this telemetersystem require no re-cycling to preserve the information therein. Thissimplifies the circuitry, however the power supply must be continuallyconnected to the memory for data preservation, but the current drain isminimal. To this end, the battery 21 within the instrument package iscontinually connected to the memory bank via lead 33. The battery lead33 is also connected to an electronic switch 25, power control circuit27, and arming circuit 29. The arming circuit 29 has its outputconnected to power control circuit 27 via lead 30. The arming circuitcontrols the application of battery power to the signal conditioningcircuits 5, to the on-board processing circuits 7, the multiplexer 9 andto analog-to-digital converter 13 via the power control circuit 27 andthe electronic switch 25. The arming circuit may, for example, includean accelerometer for sensing the set-back acceleration caused by thefiring of an artillery shell containing the instrument package, andapplying a signal to power control circuit 27 in response thereto overlead 30. The power control circuit may then apply a signal over lead 31to electronic switch 25 which will then close to apply battery power tothe four aforementioned circuit elements connected thereto over lead 35.Thus, the setback acceleration initates the processing and recording ofthe sensor outputs. The power control circuit may include circuits suchas a time delay circuit which may delay the operation of switch 25 for apredetermined time after projectile firing. It may also include a timingcircuit which may, for example, open switch 25 after a time sufficientto complete the projectile's flight, thus saving battery power and alsopreventing the further storage of sensor data in memory after theprojectile lands. The clock 23 has its output 37 connected to themultiplexer, the analog-to-digital converter and to the memory bank tosynchronize and control the operation of these circuit elements.

The circuitry of FIG. 1 is preferably packaged in a cylindrical casesuch as is illustrated in FIG. 6. The maximum inside diameter of such aninstrument package is 2 inches for most applications and this availablespace makes the use of rigid circuit boards impractical. Rigid boards insuch a space would require the use of stacked discs with all therequired interconnections between discs. Such an arrangement isdifficult to build in a shock resistant form which is required for thisinvention. The most feasible circuit arrangement is to mount thediscrete circuit components such as the memory chips or ICs comprisingthe circuit of FIG. 1 on a single flexible printed circuit board withthe components arranged in parallel rows or columns so that the boardcan be rolled parallel to the direction of the component rows andinserted into the cylindrical case as a roll, with the componentsmounted on the inside of the rolled board. Flexible circuit boards canbe rolled as much as 2 revolutions or 720° and fitted into a 2 inchdiameter housing. This configuration leaves space inside of the rolledcircuit board for the other discrete components such as the battery 21and the arming circuit 29. The cylindrical case is provided with a plugor connector at one end thereof with a wire harness connecting the plugto the terminals on the rolled circuit board. The external sensors areconnected to the telemeter's circuitry through the plug and the memorybank output is also connected thereto to facilitate the transfer of thedata therein to the portable ground unit after the projectile has landedand been recovered.

The packaging of the digital memory telemeter must be done to avoiddamage and to permit operation of the circuitry during the normal highacceleration caused by firing, flight, and projectile impact. Thisinvolves a knowledge of a shock spectrum including the duration,magnitude and the orientation of shock and acceleration forces. Forexample, the battery is perhaps the highest density item in the packageand hence it should be placed near the bottom of the cylindricalinstrument case which is located toward the aft end of the projectile.Also, the acceleration forces may displace the battery electrolyte,which can be minimized, for example, by locating the battery close tothe center of rotation of the projectile. Thus, the instrument packageshould be located along the projectile's centerline with the batterycentrally located at the aft end of the case, as illustrated in FIG. 6.Further, some capacitors with ceramic dielectrics can change value orcapacity drastically if they are not properly aligned with the set backforce vector. Further, most of the integrated circuits to be mounted onthe circuit board must have their wires or terminals hardened to preventbreakage caused by the shock of firing and flight. High-g hardeninginvolves totally encapsulating the area around the die of the componentwith a suitable potting compound. The compound must have the samecoefficient of thermal expansion as the ceramic material of the ICitself to prevent wire or terminal breakage from differential expansionor contraction of the compound and the ceramic material. A second methodwhich has been used is to employ a thin parylene conformal coating. Theprincipal benefit of using parylene is that it greatly increases thestrength of wire and lead bonds, face bonded chips, and conductorbridges. In addition, it exhibits good thermal stability, has highdielectric characteristics and acts to immobilize loose solder and wireparticles which may have been left over from manufacture.

Another way that components with high natural vibrational frequenciescan be protected is to mechanically decouple them from the metaltelemeter case in order to attenuate the excitation forces and thusprevent destructive oscillations from occurring. This can be done, forexample, by means of shock absorbing brackets on which the componentsare mounted or by the use of pads of flexible epoxy to cushion thecomponents.

FIG. 7 shows a plan view of a flexible circuit board 51 before it isrolled for insertion into the cylindrical case 63 of FIG. 6. The circuitcomponents are lined up in five horizontal rows 69 of five componentseach. The areas midway between these rows of components, indicated bythe dashed lines 67, can be flexed or bent as the flexible board isrolled up from top to bottom, or vice versa, as viewed in FIG. 7. Thesedashed line areas will contain numerous circuit board conductors, suchas 71, crossing them, however these thin flat conductors can withstandconsiderable flexing and bending without damage. The board is rolledwith the components on the inside thereof so that the outside of theroll is substantially smooth so that it can easily slide into the case,and so that connections to the plug 53 are facilitated. The assembledtelemeter system will have the aforementioned rows of componentsextending parallel to the cylinder axis.

FIG. 5 shows the rolled circuit board 51 with a connector or plug 53 atone end thereof and connected to the circuitry of the board by means ofwire harness 55. The circuit board conductors such as 59 interconnectthe circuit board terminals such as 57. The circuit board components arenot visible in FIG. 5 since they are mounted on the inside of the rolledboard.

The terminals or contacts 54 of plug 53 are connected to all of theexternally located sensors, and also the output lead 19 of the memorybank 17 is also connected thereto to facilitate the transfer of the dataafter the telemeter lands and is recovered. The plug 53 has a threadedportion 56 which engages mating threads on the inside of the case 53, asshown in FIG. 6.

The completely assembled instrument package of the present invention isshown in FIG. 6 with two broken away portions 66 and 68 to show some ofthe internal details. As stated above, the battery 21 may be centrallylocated inside the rolled circuit board and in the aft end of the case63 so that the weight thereof will not press on any other componentsduring the high set-back acceleration during firing. The component 61inside of the rolled board may be part of the arming circuit 29 ofFIG. 1. This circuit will normally include an accelerometer to respondto the set-back acceleration and initiate the operation of thecircuitry, as explained above, and the component 61 may be theaccelerometer. A broken away section of the cylindrical metal case 63 isindicated by numeral 66, and shows the outside of the rolled circuitboard which is also shown in FIG. 5, with the potting compound 65between the circuit board and the inner surface of the cylinder 63. Thispotting compound may be poured into the cylinder after all thecomponents are installed therein except for the connector or plug 53.The compound will fill all the empty space within the casing, bothinside and outside of the rolled circuit board. The broken away section68 shows both the casing 63 and the rolled circuit board broken away toillustrate the potting compound 65 inside of the roll and completelyencapsulating the component 61. The casing 63 is preferably made ofaluminum to reduce its weight.

Other shapes are possible for the metal casing, for example, it may beconical in shape if it is to fit into the nose of a projectile.

FIG. 8 shows how the data can be recovered from the instrument package64 after impact and recovery thereof. The portable interrogator unit 75has a handle 77 at the top thereof and a connector 71 on its side whichmates with the connector 53 on the instrument package. The interrogatorunit 75 has appropriate circuitry to interrogate the memory bank in thepackage and transfer the data therein to a self contained recorder suchas a tape recorder or another bank of RAM chips or ICs.

While the invention has been described in connection with preferredembodiments, obvious variations therein will occur to those skilled inthis art, in accordance with the scope of the appended claims.

What is claimed is:
 1. A recording system adapted to be carried by aprojectile during test flights and to gather data from sensors carriedby said projectile, comprising; a plurality of sensors located on saidprojectile, circuit means to process and digitize the outputs of saidsensors, and further circuit means to store said digitized sensoroutputs in a solid state digital memory.
 2. The system of claim 1wherein said circuit means and said further circuit means comprise solidstate components mounted on a flexible circuit board which is rolled andinserted into a hollow metal case, and wherein a battery and otherdiscrete components are inserted inside of said rolled circuit board,and wherein shock absorbing potting compound is poured into said caseafter all of the said circuitry and components have been insertedtherein.
 3. The system of claim 2 wherein said solid state componentsare mounted in parallel rows on said flexible circuit board and saidcircuit board is rolled parallel to said rows.
 4. An instrument packagedesigned to be carried by a projectile during test flights thereof, saidprojectile comprising a plurality of on-board sensors, said instrumentpackage comprising circuitry to process and record in a solid statedigital memory the outputs of said plurality of on-board sensors, saidcircuitry being packaged to withstand the shock of the firing, theflight, and the impact of said projectile.
 5. The instrument package ofclaim 4 wherein said circuitry comprises signal conditioning circuitsconnected to the said outputs of said sensors, a multiplexer connectedto the outputs of said signal conditioning circuits, said multiplexercomprising means to sequentially sample the outputs of said sensors inthe outputs of said signal conditioning circuits, an analog-to-digitalconverter connected to the output of said multiplexer, said convertercomprising means to digitize the output of said multiplexer to producebinary digital signals for storage in a digital memory, a digital memorybank connected to the output of said analog to digital converter, saiddigital memory bank comprising means to receive and store the digitizedsensor samples from said analog-to-digital converter.
 6. The instrumentpackage of claim 5 wherein said circuitry further comprises a battery,said battery being continually connected to said memory bank, saidmemory bank comprising one or more static random access memory chips orintegrated circuits, and means for applying the output of said batteryto the remainder of said circuitry through an electronic switch, saidelectronic switch being connected to and controlled by a power controlcircuit which is connected to and controlled by an arming circuit, and aclock connected to said signal conditioning circuits, to saidmultiplexer, to said analog-to-digital converter and to said memorybank.
 7. The instrument package of claim 5 wherein said multiplexercomprises a plurality of transmission gates equal to the number of saidsensors, and means to sequentially enable said gates to sequentiallysample the voltage output of said sensors and apply the sampled voltageto a single output lead which is connected to said analog-to-digitalconverter.
 8. The instrument package of claim 4 wherein said circuitrycomprises a flexible circuit board with discrete solid state componentsmounted thereon in parallel rows, said circuit board being rolledparallel to said rows with said components on the inside of the rolledcircuit board, said rolled circuit board being inserted into a case withfurther discrete components comprising a battery and an accelerometerlocated inside of said rolled circuit board, all of the empty spaceinside of said case being filled with a shock absorbing pottingcompound, and wherein all of said discrete solid state components arehigh-g hardened by having the dies thereof encapsulated with pottingcompound.